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EQUITY-BASED COMPENSATION - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025	Sep. 30, 2025	May 31, 2021	Sep. 30, 2020	May 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense	$ 4,619	$ 3,545	$ 9,797	$ 7,151
Income tax benefit (expense) related to equity-based compensation	$ 472	(1,165)	$ 1,202	(588)
Weighted-average grant date fair value (in USD per share)			$ 12.41
Outstanding at end of period (in shares)	8,850,572		8,850,572		7,881,236
Options exercisable at end of period (in shares)	6,800,178		6,800,178
Unrecognized compensation expense related to unvested options at end of period	$ 19,895		$ 19,895
Fair value of stock options that vested	$ 4,163		$ 4,837
2018 Equity Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant under the plan (in shares)	2,303,073		2,303,073					3,500,000
Additional Class A common shares added at the beginning of calendar year as percentage of common stock outstanding at end of previous year (percent)								4.00%
2020 Equity Incentive Award Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant under the plan (in shares)	2,021,344		2,021,344			3,000,000	1,500,000
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense	$ 1,855	1,502	$ 3,201	3,825
Period for recognition of unrecognized compensation cost (in years)			3 years 6 months
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense	$ 2,764	2,043	$ 6,596	3,326
Period for recognition of unrecognized compensation cost (in years)			2 years 7 months 6 days
Granted (in USD per share)	$ 24.06		$ 24.06
Cost not yet recognized, amount	$ 21,096		$ 21,096
Vested in period, fair value	$ 5,449		$ 9,693
Discontinued Operations, Held-for-Sale or Disposed of by Sale \| Merchant Services Business
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based payment arrangement, expense		$ 387		$ 595